On 8/31/12 7:06 AM, Bob Camp wrote:
Hi
An SC is going to have it's temperature curve centered up around 95C
or so. If it's been cut as an OCXO crystal the turns will be up there
as well. By the time it gets to room temp, the delta F / delta T is
moving mighty fast. Think in terms of multiple ppm/C. A typical cell
phone TCXO crystal is in the sub 0.1 ppm/C range in the vicinity of
room temp. In addition, SC's are pretty hard to pull. For a normal
TCXO (no DDS) something > 40 ppm of range would be needed. By the
time you get the wide tune stuff in the circuit, the phase noise
isn't going to be anything special.
Bob
We're not pulling the crystal.. we just let it sit.
What we do is change an NCO in the software radio implementation.
Typically, you have a coarse tune with a PLL in steps of 500kHz-1MHz,
and then you do the fine tune in software with a digital
mixer/downconverter and an NCO (which also is part of the carrier
tracking loop).
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
